Conventionally, a large amount of high-purity hydrogen gas is used as atmosphere gas in the semiconductor manufacturing process. Such hydrogen gas is required to contain an extremely low concentration of impurities (below ppb level) because the integration degree of semiconductor device increases.
A method of industrially manufacturing a large amount of high-purity hydrogen gas is known, in which reformed gas obtained from methanol, dimethyl ether, natural gas, and liquefied petroleum gas, etc. by steam-reforming reaction is separated into hydrogen and gas other than hydrogen by cryogenic adsorption, pressure swing adsorption, etc. to obtain hydrogen.
The cryogenic adsorption is to obtain hydrogen by circulating hydrogen-containing gas to an adsorption column filled with cryogenic adsorbent by using liquid nitrogen as refrigerant to remove impurities other than hydrogen. The pressure swing adsorption is to obtain hydrogen by repeating the processes such as pressurizing, adsorbing and desorbing impurities, and recovering adsorbent while circulating hydrogen-containing gas to a plurality of adsorption columns sequentially. The reformed gas contains carbon monoxide, carbon dioxide, methane, nitrogen, water, etc. besides hydrogen. In cryogenic adsorption and pressure swing adsorption, impurities hardly removed until the concentration of impurities is extremely low (below ppb level).
In contrast to these methods, a method of producing a relatively small amount of ultrahigh-purity hydrogen gas is known, in which raw material hydrogen containing impurities is supplied to hydrogen separation membrane formed from palladium alloy membrane to collect hydrogen from the raw material hydrogen by using the hydrogen gas permselectivity. A device for such hydrogen purification is provided with an inlet for raw material hydrogen containing impurities, an outlet for pure hydrogen, a gas passage between the inlet and the outlet, and a palladium alloy membrane in the gas passage. Such a device has a structure, for example, in which a plurality of palladium alloy capillaries (hydrogen separation membrane) each having one end being closed and the other end being opened are supported at the open end by a tube sheet and stored in a cell, and the palladium alloy capillaries and the tube sheet divide the cell into two spaces which are a primary side space (an inlet space for raw material hydrogen containing impurities) and a secondary side space (an outlet space for pure hydrogen), as shown in Patent Documents 1 to 3.